To DFW:
Your current method is how many programs that do not have a ton of money or resources handle the All-Region process. This is reality for many band programs.

If you really wanted to, you could require all of your students to have a 15-20 minute lesson with a director once a week on the all-region music. It definitely makes a difference on the end results. But it is incredibly time consuming and you have to be prepared for the very real burnout factor.